1. Field of the Invention
The embodiments to be described below generally relate to a silicon nitride wear resistant member and a method for producing the same.
2. Description of Related Art
Silicon nitride sintered compacts (sintered bodies) have been used as wear resistant members such as bearing balls and rollers utilizing the wear resistance thereof. Examples of known sintering composition of conventional silicon nitride sintered compacts include a silicon nitride/yttrium oxide/aluminum oxide/aluminum nitride/titanium oxide system (Patent Document 1: Japanese Patent Laid-Open No. 2001-328869). Sinterability is improved by using yttrium oxide, aluminum oxide, aluminum nitride, and titanium oxide as a sintering aid, thus obtaining a silicon nitride sintered compact having excellent wear resistance.
Further, Patent Document 2 (Japanese Patent Laid-Open No. 2003-34581) discloses a silicon nitride sintered compact using yttrium oxide/MgAl2O4 spinel/silicon carbide/titanium oxide as a sintering aid. In Patent Document 2, sintering temperature can be lowered to 1600° C. or less.
All the sintered compacts shown in the above Patent Document 1 and Patent Document 2 have satisfactory sinterability and excellent wear resistance. On the other hand, these conventional silicon nitride sintered compacts have high hardness and are hardly-processable materials. A wear resistant member such as a bearing ball is required to have a sliding surface which is a smooth surface having a surface roughness Ra of 0.1 μm or less. Diamond abrasive grains are generally used for processing the surface of the above silicon nitride sintered compact. However, since a conventional silicon nitride sintered compact is a hardly-processable material, there is a problem that the load of polishing is large, causing cost increase.